Impulse spectrometrs having rectilinear magnetic boundaries and an entry gap locatedthereon



Sept. 15, 1964 J. F. T. GEERK 3,149,227

IMPULSE SPECTROMETERS HAVING RECTILINEAR MAGNETIC BOUNDARIES AND AN ENTRY GAP LOCATED THERE-ON Filed June 26, 1961 2 Sheets-Sheet 1 Z M lm/euroe Sept. 15, 1964 Filed June 26,

J. F. T. GEERK 3,149,227 IMPULSE SPECTROMETERS HAVING RECTILINEAR MAGNETIC BOUNDARIES AND AN ENTRY GAP LOCATED THEREON 1961 2 Sheets-Sheet 2 United States Patent llVIPULSE SPECTROMETERS HAVING RECTI- LINEAR MAGNETIC BOUNDARIES AND AN ENTRY GAP LOCATED THEREON Jens F. T. Geerk, Weil am Rhine, Germany, assignor to Atlas-Werke Aktiengesellschaft, Bremen, Germany, a joint-stock company of Germany Filed June 26, 1961, Ser. No. 120,893 2 Claims. (Cl. 250-419) The invention relates to impulse spectrometers having rectilinear boundaries of the analytical magnetic field and an entry gap located upon the field boundary.

In the accompanying drawing FIGURE 1 schematically illustrates a known impulse spectrometer of the kind referred to in brief as 180 spectrometers. In such spectrometers the ion bundle is injected into the entry gap E perpendicular to the field boundary (e:0) and the (straight) image line g coincides with the field boundary :0) It has been found that such known spectrometers contain an undesirably large aperture error. It is an object of the present invention to reduce the aperture error.

According to the invention there is provided an impulse spectrometer having an analytical magnetic field with a rectilinear boundary and an ion entry gap located on the field boundary, wherein the central ray of the bundle of ions passing through the entry gap is arranged to form with the perpendicular to said boundary an injection angle (2) where 0 e 54, and wherein the straight line on which lie the image points of the individual bundles of ions separated according to their masses, passes through the entry gap.

For a better understanding of the invention and to show how to carry the same into effect reference will now be made to FIGURES 2, 3 and 4 of the accompanying drawing in which:

FIGURE 2 shows the scheme of an impulse spectrometer system having an image line angle :9.4" and an injection angle e:l0,

FIGURE 3 shows the scheme of an impulse spectrometer having the optimum image line angle 'y:l9 28 and the injection angle e=35 16,

FIGURE 4 shows a graph of second-order aperture errors and injection angle e.

The conventional mass spectrometer system illustrated in FIG. 1 operates with an injection angle e:0 with respect to the perpendicular to the field boundary x. The injection gap E is located at the field boundary. The ion bundles injected into the magnetic field are deflected by 180, and mass spectrometric representation occurs on an image line g coincident with the field boundary x. The angle between the field boundary and the image line is thus 'y:0.

FIGURE 2 shows a spectrometer having an injection angle e=l0. This provides an angle of inclination :9.4 on the part of the image line g. The focussing of this spectrometer is still of the first order, but the aperture error is smaller than in the case of the 180 mass spectrometer. From FIGURE 4 the error is 91% of the 180 spectrometer. If the injection angle 6 is now made still larger, an image line g having a larger 7 is obtained. The image line/ field boundary angle reaches a maximum of 'y=19 28 at an injection angle e=35 16' (FIG. 3). The second-order aperture error now becomes zero (second-order focussing). If the injection angle is made still larger, e.g. e=40, then 7 grows smaller once more ('y 19 28') (therefore one picture line continues to pass through the entry gap). The aperture error once more becomes greater, and we again have first-order focussing. The system e:35 16' of maximum inclination with respect to the field boundary of the image line passing through the entry gap, 19 28, is therefore the most advantageous of all mass spectrometers of the type straight field boundary with entry gap on the field boundary and image line passing through the entry gap. Exploration or mensuration of the mass spectrum is effected (as shown in FIGURE 3) in that the target gap A together with the target b and the amplifier valve 0 is moved along the image line g. Since in the case of the impulse spectrometer in accordance with the invention, the enlargement is constant:1 over the entire mass range, the movable target gap A is equally suitable for all masses.

The angle 7 and the second-order aperture error as a percentage of the aperture error i of the 180 spectrometer are plotted in FIG. 4. The two graphically illustrated functions for the totality of systems having one (straight) image line are:

sin 26 'Y 3 00s 2 e f:/3 cos 6 2/.100

As will be seen from FIGURE 4, when the injection angle is modified to for instance e:10, the image line g passing through the entry gap E is inclined at an angle 'y:9.4 to the field boundary; the second-order aperture error now amounts .to only 91% of the aperture error of the 180 spectrometer. At an injection angle e:50, the image line is inclined at 7:173", and the second-order aperture error is of that of the 180 spectrometer. Any injection angle between 0 and almost have a corresponding specific angle of inclination of the associated image line passing through the entry gap.

The maximum angle of inclination of the image line in this unidimensional set (00 of optical systems yields especially advantageous design and is possessed by the impulse spectrometer according to the invention, in which 'y=l9 28' with an injection angle 6:35 16. A particular feature is, however, that such an ion optical system has the smallest aperture error of any system in the above defined unidimensional set of ion optical systems. FIG- URE 4 shows that within the set of unidimensional systems characterised by the injection angles 6 0 to e:54, the 180 spectrometer possesses the greatest second-order aperture error; it is only from 6:54 44' that the secondorder aperture error rises above that of the 180 spectrometer, until it reaches a maximum of 200% when e:90 (glancing injection). In the case of the system according to the invention, where "y=l9 28', the secondorder aperture error is zero. This constitutes the essential technical advance of the system according to the in vention as compared with the convetnional 180 system and with all other systems having one (straight) image line.

With the impulse spectrometers according to the invention it is possible to arrange the entry gap a short distance away from the field edge, so that the arms do not lie in the strongest scatter field of the magnet prior to their emergence from the entry gap. This measure merely results in the image line being moved slightly parallel to itself in the opposite direction to the ion movement.

I claim:

1. spectrometric apparatus comprising,

means defining an entrance slit,

means defining a magnetic field bounded by a substantially straight line substantially passing through said entrance slit for deflecting particles entering said field through said entrance slit back across said line at points thereon spaced from said entrance slit by a distance related to the mass of the respective particles,

a source of a beam of said particles directed through said entrance slit into said field,

the entrance angle formed by said beam and the nor- 3;149,2a7 v 2 3 a 4 mal to said slit and said line being greater than zero said exit slit for receiving particles of a common and less than 54 44, mass passing through said exit slit.

means defining at least one exit slit outside said mag- Spfictfometfic pp s in accordance With Claim netic field along the image line representative of the 1 Whflein Said entrance angle is Substantially image of saidentrance slit Where particles of the 5 a same mass are focussed substantially into a point on References cued m the file of thls. patent said imagetline by said fie1d,- UNITED STATES PATENTS said image line forming an acute angle with said snb- 1 2,709,222 Lawrence May 24, 1955 tantially straight line, 2,911,532 Tipotsch Nov. 3, 1959 10 2,922,882 Barnes Jan. 26, 1960 and means defining a target immediately adjacent to 

1. SPECTROMETRIC APPARATUS COMPRISING, MEANS DEFINING AN ENTRANCE SLIT, MEANS DEFINING A MAGNETIC FIELD BOUNDED BY A SUBSTANTIALLY STRAIGHT LINE SUBSTANTIALLY PASSING THROUGH SAID ENTRANCE SLIT FOR DEFLECTING PARTICLES ENTERING SAID FIELD THROUGH SAID ENTRANCE SLIT BACK ACROSS SAID LINE AT POINTS THEREON SPACED FROM SAID ENTRANCE SLIT BY A DISTANCE RELATED TO THE MASS OF THE RESPECTIVE PARTICLES, A SOURCE OF A BEAM OF SAID PARTICLES DIRECTED THROUGH SAID ENTRANCE SLIT INTO SAID FIELD, THE ENTRANCE ANGLE FORMED BY SAID BEAM AND THE NORMAL TO SAID SLIT AND SAID LINE BEING GREATER THAN ZERO AND LESS THAN 54* 44'', MEANS DEFING AT LEAST ONE EXIT SLIT OUTSIDE SAID MAGNETIC FIELD ALONG THE IMAGE LINE REPRESENTATIVE OF THE IMAGE OF SAID ENTRANCE SLIT WHERE PARTICLES OF THE SAME MASS ARE FOCUSSED SUBSTANTIALLY INTO A POINT ON SAID IMAGE LINE BY SAID FIELD, SAID IMAGE LINE FORMING AN ACUTE ANGLE WITH SAID SUBTANTIALLY STRAIGHT LINE, AND MEANS DEFINING A TARGET IMMEDIATELY ADJACENT TO SAID EXIT SLIT FOR RECEIVING PARTICLES OF A COMMON MASS PASSING THROUGH SAID EXIT SLIT. 